Foam materials are a class of commercially and industrially important chemical-based materials. Foams can be prepared by aerating a foaming composition (i.e., entrapping air in a foaming composition), which can be derived by diluting a concentrated precursor. Many foams require certain physical properties to be appropriately useful in desired applications. Among preferred physical properties for foams is the property of stability, to allow the foam to be in a useful form over an extended period of time and therefore useful where an especially stable foam can be desirable, e.g., fire prevention, fire extinguishment, vapor suppression, freeze protection for crops, etc.
An important class of commercial foams includes aqueous film-forming foams (e.g., AFFFs), aqueous compositions typically containing fluorochemical surfactant, non-fluorinated (e.g., hydrocarbon) surfactant, and aqueous or non-aqueous solvent. These foams can be prepared from concentrates by diluting with water (fresh or sea water) to form a "premix," and then aerating the premix to form a foam. The foam can be dispersed onto a liquid chemical to form a thick foam blanket that knocks down a fire and extinguishes the fire by suffocation. These foams also find utility as vapor suppressing foams that can be applied to non-burning but volatile liquids, e.g., volatile liquid or solid chemicals and chemical spills, to prevent evolution of toxic, noxious, flammable, or otherwise dangerous vapors.
Individual components of a foaming composition contribute toward different physical and chemical properties of the premix and the foam. Fluorinated and non-fluorinated surfactants can exhibit low surface tension, high foamability, and good film-forming properties, i.e., the ability of drainage from the foam to spread out and form a film over the surface of another liquid. Organic solvents can be included to promote solubility of surfactants, to promote shelf life of the concentrate, and to stabilize the aqueous foam. Thickening agents can be used to increase viscosity and stability of the foam.
Especially preferred properties of foams are stability, vapor suppression, and burnback resistance. Stability refers to the ability of a foam to maintain over time its physical state as a useful foam. Some fire-fighting foams, e.g., foams prepared from foaming premix compositions containing surfactant and hydrated thickener, are stable for periods of hours, or less than an hour, and are often regularly reapplied. Longer periods of stability can be achieved by adding ingredients such as reactive prepolymers and crosslinkers, polyvalent ionic complexing agents, proteins, etc.
There exists a continuing need for foaming compositions, foam compositions, and methods of preparing foaming compositions and foams useful for application to a liquid chemical or another substrate which may be volatile, flammable, otherwise hazardous, or not hazardous at all but desirably protected from potential ignition. This includes a particular need for preparing foam compositions that are stable in the form of a useful foam for extended periods of time, e.g., up to or greater than 12, 24, or 36 hours.